//https://leetcode.cn/problems/unique-binary-search-trees/

class Solution {
public:
    int numTrees(int n) {
        vector<int> dp(n + 1);
        dp[0] = 1;

        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= i; j++)
                dp[i] += dp[j - 1] * dp[i - j];

        return dp[n];

    }
};